Prior art on high molecular weight polymers for the slow release of drugs is extensive. Such polymers are normally encapsulated products that are used in nonaqueous systems and depend upon biodegradability to be effective. They are not effective in releasing materials into aqueous systems at ambient temperatures, i.e., 15.degree.-60.degree. C.
Low molecular weight oligomers have been claimed in U.S. Pat. No. 4,715,967 for release of hydroxyacetic acid/lactic acid from powders. The polymers function as plugs or filters and are used at temperatures above 150.degree. C. No ingredients are claimed and the polymers are essentially crystalline containing greater than 85 per cent of hydroxyacetic acid, the balance lactic acid. The compositions of U.S. Pat. No. 4,715,967 have too slow a degradation rate to be used as a matrix. Their melting points are too high to be capable of blending chemicals without their degradation.
Polyester polymers of hydroxyacetic acid with lactic acid are taught by U.S. Pat. Nos. 4,387,769 and 4,526,695 as oil well treating agents. These polymers were extensively studied in the 1950s as possible textile fibers until it was found that they readily hydrolize in the presence of heat and water. They degrade in the presence of water at elevated temperatures like 150.degree. C. and above in about one to seven days to form oligomers. These polyester polymers are expensive to manufacture and are of limited effectiveness in low temperature applications. Major problems in the control release art continues to be the inconsistency of dispensing rates and the erratic longevity of the cakes or blocks because of rapid and uneven dissolution resulting in decreased cake stability and longevity.
It is an object of the present invention to provide molded compositions comprising an oligomer binder which is water-degradable, environmentally acceptable, and resistant to fragmentation, which compositions are suitable for use for dispensing chemical agents at a controlled rate into toilet tanks or any other water-containing reservoirs, e.g., cisterns, lakes, ponds and pools, over extended periods of time and at ambient temperatures.
It is a further object of the present invention to provide solid unsupported compositions which comprise as a matrix certain hydroxyacetic acid/lactic acid polymer along with a dye, a fluorosurfactant, a quaternary ammonium salt and an inorganic salt.
Other objects, advantages and novel features of the present invention will be apparent to those skilled in the art from the following description and appended claims.